Ultraviolet apparatus for disinfection and sterilization of fluids

ABSTRACT

An ultraviolet sterilization and disinfection system for fluids which includes apparatus for sensing selected operating characteristics such as physical characteristics of the fluid to be disinfected or sterilized and the operating conditions of the ultraviolet sources proportioning these variable and generally non-linear parameters and modifying such factors as fluid flow, ultraviolet energy imparted to the fluid to insure destruction of selected organisms without the use of excessive energy. Control may also be provided for the admission of selected quantities of disinfecting chemicals such as chlorine to the fluid.

This application is a division of application Ser. No. 141,558 filedApr. 18, 1980 entitled "Method and Apparatus for Disinfection andSterilization of Fluids", now U.S. Pat. No. 4,336,223 issued June 22,1982.

This invention relates to the disinfection and sterilization of fluidsand more specifically to a novel and improved method and apparatus forthe disinfection and sterilization of fluids utilizing ultravioletradiation devices which extends the life of such devices, conservesenergy and at the same time insures reliable and uniform treatment ofthe fluids at all times. The invention further contemplates theutilization of controlled chemical treatment in combination withultraviolet radiation which results in operating efficiencies far inexcess of either procedure alone.

The effectiveness of ultraviolet radiation in the sterilization offluids is well known and a wide variety of systems have been developedfor the sterilization of water for both commercial and residentialapplications. Known ultraviolet sterilization systems are generally ofthe brute force type limited to specific operating range limits ofturbidity, flow rate, temperature and the like to provide ultravioletexposure considered to be sufficient to insure desired sterilization forat least the major portion of the ultraviolet lamp life. Since theradiation intensity of the ultraviolet lamps decreases with use, knownsystems are generally designed for proper sterilization near the end ofthe lamp life with the result that excess operating energy is used whenthe lamps are new. Furthermore, known systems are designed for specificranges of turbidity and flow rates to insure satisfactory operation andunexpected changes will result either in failure to properly sterilizeor in the use of excessive energy.

The control system in accordance with the invention becomes increasinglyimportant from the standpoint of both reliability and economy in thetreatment of lower quality and larger quantities of water. With thisinvention, lamp life as compared with brute force systems is greatlyincreased and at the same time substantial reductions in energyrequirement are effected. At the same time, great reliability is insuredsince the required energy (radiation intensity and time of exposure) isimparted to the liquid at all times. Accordingly, this invention has asone of its objects the provision of a novel and improved method andapparatus for the sterilization of fluids which not only insures propersterilization but also attains that end by controlling lamp power,waveform and starting conditions and modifying lamp power or intensityin accordance with physical conditions, such as flow rate, temperature,turbidity and the like of the fluid. In this way, the apparatus willprovide the threshold of energy necessary for the destruction ofselected undesirable organisms and viruses over a wide range of fluidcharacteristics and operating conditions. At the same time, the entireoperation can be terminated substantially instantaneously should theultraviolet radiation source or sources be incapable of imparting therequired energy to the fluid.

Another object of the invention resides in the provision of a novel andimproved method and apparatus for the sterilization of fluids which notonly greatly increases lamp life while affording the ultraviolet energyfor the destruction of microorganisms but in instances wherein fluidflow and quality vary over wide limits the conservation of energythrough the use of this invention can be a more economical substitutefor chemical disinfection treatments than known ultravioletsterilization methods and apparatus.

Still another object of the invention resides in a novel and improvedmethod and apparatus for the sterilization of fluids and particularlyliquids which affords not only increased lamp life but a substantialsaving in energy by a continuous modulated control of the energythreshold and exposure as the fluid characteristics, such as flow,turbidity and other conditions change.

Still another object of the invention resides in a novel and improvedmethod and apparatus for the sterilization of fluids wherein theultraviolet energy imparted to the fluid and/or the rate of flow of thefluid can be controlled to insure proper sterilization. For instance,instead of maintaining uniform flow and modifying the energy imparted tothe fluid in accordance with changes in the characteristics of thefluid, the ultraviolet lamps can be operated at maximum intensity andthe flow can be controlled to insure proper sterilization.

A further object of the invention resides in the provision of a methodand apparatus for the disinfection and sterilization utilizing thecombined effects of both chemical and ultraviolet systems. With thenovel and improved control system in accordance with the invention,measured quantities of a suitable chemical such as chlorine can beintroduced into the liquid depending on the liquid characteristics andflow. With this arrangement, disinfection by the chemical continuesbeyond the ultraviolet treatment and the combined cost of the chemicaland electrical energy is substantially less than the cost of eithersystem alone. In many applications, the resultant cost can be less than20 to 25 percent of the cost of either system. Thus, not only isconsiderable economy realized by this synergistic effect but residualchlorine can be maintained within tolerable limits. The inventioncomprises a novel and improved ultraviolet sterilization system forsterilization of fluids embodying ultraviolet generating means capableof producing a desired energy threshold and exposure for said fluidsunder adverse conditions of fluid quality throughout the life of thelamps, means for continuously monitoring at least selectedcharacteristics of the fluid and radiant energy emitted from thegenerating means, means for modifying the magnitude of ultravioletradiation in accordance with the monitored characteristics to providethe desired energy threshold and exposure to effect sterilization andcontrolling the characteristics of the energy supply to the generatingmeans to maximize further the life of the generating means. Theinvention further provides a system for controlling fluid flow inaccordance with changes in fluid characteristics while maintainingultraviolet energy at a maximum or in the alternative modifying fluidflow if the ultraviolet intensity and exposure time is insufficient toachieve proper sterilization. Means are also provided for controllingthe admission of a disinfecting chemical to the liquid in accordancewith liquid characteristics while at the same time sterilizing theliquid with controlled ultraviolet radiation.

The above and other objects and advantages of the invention will becomemore apparent from the following description and accompanying drawingsforming part of this invention.

IN THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of the apparatus for thesterilization of fluids utilizing ultraviolet radiation:

FIG. 2 is a plan view of a portion of the apparatus illustrated in FIG.1;

FIG. 3 is a side elevational view of FIG. 2 with the housing wallremoved;

FIG . 4 is a cross sectional view of FIG. 3 taken along the line 4--4thereof;

FIG. 5 is a cross sectional view of FIG . 2 taken along the line 5--5thereof;

FIG. 6 is a perspective view of the structure shown in FIG. 2 withsections taken along the lines 6--6, 6--6 thereof;

FIG. 7 is a fragmentary end view of FIG. 2 taken in the direction ofarrow 7; and

FIG. 8 is a block diagram illustrating the circuitry for controlling theintensity of the radiation produced by the ultraviolet radiationsources.

FIG. 9 is a graph which shows a typical example of the power demand tomeet variations normally experienced in the ultraviolet radiationsterilization of liquids.

The effectiveness of ultraviolet radiation for the sterilization offluids and particularly water has been recongized for many years. Knowndevices utilizing ultraviolet radiation embody appropriate means for thecirculation of the liquid in close proximity to ultraviolet lamps inorder to expose all of the liquid to the radiation and at the same timeprovide the desired exposure to effect the destruction ofmicro-organisms. The design concept of such systems, however, involvedthe determination of the radiation intensity of the lamps at or near theend of the lamp life and sufficient lamps were provided to obtain thenecessary exposure time to effect the desired sterilization. Under thoseconditions, new lamps therefore afforded radiation intensities far inexcess of that required to effect the desired sterilization. Suchprocedures while being generally satisfactory for use with liquidshaving known physical and chemical characteristics are not reliableunder conditions wherein the characteristics of the liquid are subjectto variations. Moreover, even under conditions wherein some control isexercised over the characteristics of the liquid, insufficient radiationmay, nevertheless, be experienced particularly toward the end of thenormal lamp life. To compensate for such deficiencies in known systems,efforts have been made to insure the provision of radiation intensitiesand exposure far in excess of that which would be normally required toeffect the desired ends. The efficiencies of known systems, therefore,are not only poor as far as energy consumption is concerned butoperation of the lamps at maximum intensity at all times also materiallyshortens the life of the lamps. Moreover, known systems do not providefor unexpected variations of water characteristics, flow rate and thelike and should the ultraviolet lamps be nearing the end of their normallife and if water turbidity for instance should change materially, it ismost likely that proper sterilization will not be effected. With thisinvention, however, effective sterilization is insured notwithstandingchanges in the water even though they may vary over wide ranges withindesign limits that may be selected. Should such variations exceed designlimits, an alarm can be provided and termination of the processeffected. With the method and apparatus according to the invention,sterilization can be attained at a cost competitive with and often farless then chemical treatment.

It is well recognized that a wide variety of structures may be employedfor the purpose of subjecting fluids and specifically water toultraviolet radiation for the purpose of sterilization. One suchstructure, as illustrated in the drawings, provides for the flow ofwater lengthwise of elongated ultraviolet radiating lamps through it isevident that the water can be directed transversely of the lamps, socalled laminar flow, and that other lamp configurations may be employed.

Referring now to the drawings and more specifically to FIGS. 1 through7, the illustrated embodiment of the invention includes a housing 10containing the ultraviolet sterilizing apparatus generally denoted bythe numeral 11. The apparatus 11 is shown and illustrated indiagrammatic form in FIG. 1 while in the remaining figures details ofthe structure are illustrated. Referring to FIG. 1, a water inletconduit 12 is connected to one side of the header 13. The water thenflows to the right through tubes 14 and 15 into the header 18 thencethrough tubes 16 and 17 for return to the header 13 and dischargethrough the outlet conduit 19. The inlet circuit 12 includes a pluralityof sensors to determine certain physical characteristics of the liquidto be treated. In the instant embodiment of the invention, thetemperature sensor 20 having leads 20a extending therefrom records thetemperature of the liquid in the inlet. This sensor is followed by aturbidity sensor consisting of a suitable light source 21 having leads21a extending therefrom for energizing the light source and aphotoelectric sensor 22 having leads 22a extending therefrom. The flowdetector is denoted by the numeral 23 having leads 23a and theconductivity detector is denoted by the numeral 24 having leads 24aextending therefrom. These measurements made by the sensors areutilized, as will be discussed in connection with FIG. 8, to effect incombination with other measurements, the operation of the ultravioletradiation sources.

Referring more specifically to FIGS. 2 through 7, the headers 13 and 18are essentially of rectangular configuration with the header 13 havinglongitudinal bores 25 and 25' extending inwardly from opposing ends topoints spaced from the center to provide a central barrier 25a. The face27 of the header 13 has four openings each denoted by the numeral 28 forfrictionally receiving one end of each of the tubes 14 through 17. Asuitable sealing compound may be employed to insure water tight joints.Similarly, the face 29 of the header 18 has a plurality of correspondingopenings 30 to receive the opposing ends of the tubes 14 through 17 inlike manner. The headers 13 and 18 with the tubes 14 through 17 disposedtherebetween are then held in position by a plurality of bolts 31 asviewed more clearly in FIGS. 2 and 3.

Tubular elements formed of quartz or other suitable radiationtransparent material and denoted by the numeral 32 extend through eachof the tubes 14 through 17 and through cooperating openings 33 in thewall 34 of the header 13 and similarly through openings 35 in the wall36 of the header 18. It will be observed that the tubes 32 protrudeslightly beyond the walls 34 and 36 of the headers 13 and 18 and areheld in position by annular caps 37 and 38. Each tubular element 32 issealed by an O-ring 39 as illustrated more clearly in FIG. 5. Morespecifically, each of the caps 37 as well as the caps 38 on the header18 has an enlarged opening 40 for slidably receiving the tubular element32. The remainder of the opening 41 through each cap 37 and 38 isapproximately equal to the inside diameter of the element 32 and thecaps 37 each include three or more spacing elements 42 to center tubularlamps 44 through 47 within openings 41 of the caps 37 by engagement withthe lamp ferrals 43 on one end of each lamp. Since the ferrals 43 on theother end of each lamp are centered by fixedly positioned sockets, aswill be described, air can readily circulate in the space between eachlamp and the associated surrounding element 32. Each of the caps 37 and38 is held in position by screws 48 as will be observed more clearly inFIG. 7.

As previously mentioned, the ultraviolet radiation sources 44 through 47are in the form of tubular structures having an elongated radiationtransparent tube 49 carrying tubular ferrals 43 on each end thereof.Cylindrical terminals 51 extend from each end of each lamp forengagement with sockets as shown in FIGS. 2 and 3. In these figures, itwill be observed that an elongated channel member 53 is disposedparallel to the header 18 and carries insulated sockets 54 in spacedrelationship to the wall 36 of the header 18. The channel member 53 isheld in precisely spaced relationship by a pair of bolts 53'. Each ofthe sockets 54 is precisely aligned with the axis of the associatedradiation transparent tube 32 so that a lamp inserted from the left sideof the structure as shown in the figures will frictionally engage theassociated socket 54 and thus maintain the lamp in proper positionwithin the apparatus. Similar sockets 55 individually engage terminals51 on the left end of the ultraviolet lamps as illustrated.

It is often desirable to control the turbulence of the liquid beingtreated with apparatus in accordance with the invention though it isdesirable to avoid devices that will function to impede or otherwiseresist the flow of the liquid. In the instant embodiment of theinvention, turbulence can be controlled by adjusting the curvatures ofthe liquid flow path within the headers 13 and 18. In addition,turbulence can also be controlled by utilizing movable closure elements56 on each end of the header 18. In this instance, it will be observedthat the closures 56 are sealed to the inner bore of the header 18 byO-rings 57 and suitable means may be provided for moving the closures 56inwardly and outwardly of the ends of the header 18. In this way,turbulence can be controlled without imparting any significantresistance to the flow of the liquid through the apparatus.

FIGS. 2, 3, 5 and 7 illustrate additional sensing devices for use in thecontrol of the energy fed to the ultraviolet lamps 44 through 47. It waspreviously pointed out in connection with FIG. 1 that sensors formeasuring liquid temperature, flow, turbidity and conductivity playedimportant roles in controlling the intensity of ultraviolet radiationand exposure time in order to insure proper sterilization of the liquid.In addition to those factors, it is desirable to measure continuouslythe operating conditions of the ultraviolet lamps as well as thepenetration of the ultraviolet radiation through the liquid surroundingeach of the lamps. For instance, measuring the ultraviolet radiationdirectly from the lamp surface will provide a continuous indication ofthe intensity of the radiant energy while measurement of the ultravioletradiation at the surface of the liquid through windows in the liquidconducting tubes 14 through 17 will indicate the degree of absorption ofthe radiation by the liquid. Insufficient intensity at the surface ofthe liquid will therefore necessitate either increase in the intensityof the radiation or in the alternative an increase in the exposure time.The temperature at the surface of each lamp will insure proper operationof the lamps. For instance, the temperature of a lamp may change withlamp current and if the lamp temperature should increase beyond a knownoptimum value, the intensity of the radiation will decrease.Furthermore, lamp temperature provides an indication of ambienttemperature conditions which can be adjusted to attain the desiredoperating temperature for the lamps. Accordingly, lamp temperatureconstitutes a significant factor and insures efficient operation of theapparatus.

The sensing devices for lamp temperature, intensity of radiation at thesurface of the lamp and intensity of radiation at the surface of theliquid are shown in FIGS. 2, 5 and 7. The sensor for measuring lamptemperature is shown more clearly in FIG. 5 and comprises a thermistor58 or other suitable device carried by an L-shaped bracket 59 having oneleg 60 secured to the cap 37 by means of a screw 61 and a second leg 62extending in the space between the lamp 44 and the surrounding radiationtransparent tube 32. The thermistor 58 is carried at the inner end ofthe leg 62 and the wires 58' from the thermistor 58 would normally becarried by the bracket leg 62 and properly insulated therefrom. Thebracket 62 is formed of resilient material so that when the lamp 44 isin place the thermistor 58 will bear tightly against the lamp surfaceand at the same time the resiliency will permit the lamp to be readilywithdrawn for repair or replacement. Lamp intensity is measured by asuitable photo detector 63 carried within an opening 64 in mainfold 13.If desired, the radiation intensity sensor 63 may include a suitablefilter that will pass only a selected radiation bandwidth found mosteffective for a selected sterilization process. Any deviation of thelamp from the selected bandwidth will immediately indicate a loss ofradiation and this condition can be rectified by proper adjustment oflamp current and/or voltage unless of course the lamp is near the end ofits life which factor can also be determined by the relationship of lampintensity to lamp temperature, current and/or voltage.

The intensity of the radiation at the outer surface of the liquidflowing through the tubes 14 through 17 is measured by a photo detector65 mounted on the surface of each of the tubes 14 through 17. For thispurpose, each of the tubes is provided with a window 66 to which thephoto detector or other equivalent device is secured. As in the case ofthe intensity measuring device 63, the device 65 may also be providedwith a suitable filter. In this way, adequate penetration of the liquidby the radiation can be assured throughout the entire sterilizingprocess.

As previously mentioned, the effectiveness of ultraviolet radiation inthe destruction of micro-organisms and viruses is known. It is alsoknown that ultraviolet radiation of the order of 2,537 angstroms is themost effective germicidal wavelength and that ultraviolet energy isgenerally given in terms of micro-watt seconds per square centimeter.Published information is generally available indicating the total energyrequired for the destruction of selected micro-organisms and such energyranges from as low as 1,600 micro-watt seconds per square centimeter for90 percent effectiveness against certain organisms to as much as 440,000micro-watt seconds per square centimeter for other organisms forcomplete colonization destruction. Utilizing known ultravioletsterilizing systems which are essentially all of the brute force type,the inefficiencies are of such great magnitude that ultravioletsterilization processes have been restricted by cost effectiveness ascompared with known conventional chemical treatments such as treatmentutilizing chlorine. With the instant invention however, the apparatus isnot only controlled to provide only that power necessary to destroyselected micro-organisms but the adjustment can be modified duringoperation in the event more or less energy is required for thedestruction of the organisms. It has also been found, as previouslypointed out, that the life of ultraviolet lamp sources can be more thandoubled by controlling both lamp current and voltage to provide onlythat radiation intensity necessary for achievement of the objects of theapparatus. With this invention, efficiencies of the order of one hundredtimes those attainable with known apparatus can be achieved and in manycases enables ultraviolet sterilization to be economically competitivewith chemical processes. The importance of this invention becomes evenmore evident upon consideration of the adverse effects of chlorine onthe human body not to mention taste when chlorine is utilized forsterilization of drinking water. Chlorine is also being foundparticularly disadvantageous because of the results of research showinga connection between cancer and chlorination when combined with otherchemicals found in water. Further, the cost of chlorine has beenconstantly increasing, chlorine control presents serious complicationsboth in metering as well as its deleterious affect on water handlingequipment.

FIG. 8 shows a block diagram of one circuit for automaticallycontrolling the intensity of radiation from the ultraviolet radiationsources in accordance with the invention. It will be observed that amicroprocessor 70 is utilized to perform the basic functions of logicand forms part of the basic control 71 which includes the memory addressbus 72, a random access memory (RAM) 73, a programmable read only memory(PROM) 74, a read only memory (ROM) 75 and a clock 70'. A self containedbattery 76 is used as a constant standby source for the random accessmemory.

The information pertaining to the characteristics of the fluid beingsterilized or disinfected is fed from the sensors 20, 22, 23 and 24through the leads 20a, 22a, 23a and 24a to the multiplexing gates 77 andrepresent temperature, turbidity, flow and conductivity respectively.The blocks 44 through 47 represent the measuring devices associated withthe four ultraviolet radiation lamps 44 through 47 and the blocks aredenoted by the same numerals utilized to denote the lamps. For instance,the lead 58a coupling the block 44 to the multiplexing gates 77 providesa signal proportional to lamp temperature. The lead 63a provides asignal proportional to intensity of radiation measured at the surface ofthe radiation transparent element 32, the lead 65a provides a signalproportional to radiation intensity at the surface of the fluid whilethe leads 44a and 44b provide signals proportional to current andvoltage respectively in the lamp 44. The signals from the sensorsassociated with lamps 45 through 47 are similarly denoted by thesubscripts b, c and d respectively except for the lamp current andvoltage which leads are denoted by the numerals 45a, 46a, 47a, 47 a and45b, 46b and 47b respectively.

The multiplex gates 77 feed information to the data bus 78 and throughan analog to digital convertor 79 to the microprocessor 70. A keyboard80 and display 81 are connected to the data bus 78 together with analarm 82. Lamp control information is fed from the microprocessor 70through the digital to analog converter 83 to the multiplex gates 84.There is also a coupling between data bus 78 and the microprocessor 70to provide for the transmission of information to the microprocessor viathe keyborad and for retrieving information for presentation on thedigital display 81 and a coupling between the data bus and multiplex

The multiplex gates 84 produce lamp control signals which are fed tocontrol devices 85 through 88 such as Triacs or other similar devices.AC power is fed to the Triacs 85 through 88 via the leads 89, 90, 91, 92and 93 and the power outputs from the Triacs 85 through 88 are fed toballasts 94 through 97. The ballasts are required for starting the lamps44 through 47 and maintaining the ionization within each lamp afterstarting has been completed.

It has been found that the life of ultraviolet lamps is materiallyaffected by the characteristics of the energy utilized for starting thelamp and maintaining its operation. More specifically, sharp transientsin the energy applied to ultraviolet lamps materially shorten the lifeof the lamps and accordingly the energy from each ballast 94 through 97is each fed through an individual filter 98 through 101 for removal ofenergy peaks. For this purpose, the filters would be either low-pass orband-pass filters which are tuned to remove all frequencies greater thanthe frequency of the AC power. The outputs from the filters 98 through101 are fed through leads 54a and 55a to the lamp 44, 54b and 55b to thelamp 45, 54c and 55c to the lamp 46 and 54d and 55d to the lamp 47.Suitable devices 44a through 47a are interconnected with the leads 55athrough 55d to produce current signals which are fed to the multiplexinggates 77. Similarly, voltage signals are obtained from the filters 98through 101 via the leads 44d through 47b which are also fed to themultiplexing gates 77. In this way, both voltage and current in thelamps can be controlled as it has been found that through carefulcontrol of both starting and operating voltages and currents as well asmaintenance of a proper waveshape, lamp life can be significantlyextended.

It is to be understood that the foregoing block diagram presents onlyone embodiment of a possible circuit arrangement utilizing amicroprocessor for achieving modulated power control of the ultravioletlamps. As mentioned, the sensors each produce an analog voltage which isadjusted to vary over a predetermined range. The analog and digitalconvertor 79 codes these inputs for transmission to the microprocessor70. The ROM would preferably be preprogrammed with an executive programwhich constitutes the basis for the microprocessor functions. The PROM74 provides for auxiliary functions which may be unique to a particularinstallation. The input to this memory is by way of the keyboard 80 orother similar alpha-numeric thermal. Control items such as time of dayor related timing functions may be entered into storage in this way.Variable data which may be required for computation is stored in therandom access memory 73.

The microprocessor 70 utilizes a clock 70' as the time base for allinternal functions and compares the value of the various inputs withestablished limits set in the memory. Off normal values provides analarm output indicating an abnormal or undesired condition of operation.The display 81 which may also include a data printer can provide data inresponse to a code introduced by the keyboard 80 so that an operator cancheck on any specific condition of the operation as for instance theultraviolet intensity of each lamp.

The output from the microprocessor is then converted by the digital toanalog convertor 83 and functions through the multiplexing gates 84 toconstantly adjust the magnitude of the voltage fed to each of the lamps44 through 47.

In addition to the factors introduced into the computer as illustratedin FIG. 8 for control of radiation intensity, other factors such as thedeposit of materials on the quartz elements 32 surrounding the lamps canbe introduced as constants or measured values and may be utilized tooperate a suitable cleaning mechanism which would automatically removedeposits periodically. This may be an important factor in manyapplications in as much as it affects the transparency of the tubularelements 32.

To illustrate the importance of this invention, let it be assumed that asterilizer is required under ideal conditions to sterilize a clearliquid having a fixed flow of a hundred liters per minute (38,000gallons per day). Under the conditions, the input power required wouldbe approximately 200 watts or 4.8 KW/hrs. per day. However, it is wellrecognized that ideal conditions do not always exist and that avariation in turbidity, less than ideal operating conditions includingolder lamps, unclean lamp protecting elements an off optimum temperaturecan require as much as 75 times the power required for the ideal caseeven assuming constant flow. Under these conditions, as much as 15 KWinput would be required or approximately 360 KW/hrs. per day. In thisone instance, it can be seen that through the control of the intensityof the radiation to provide only that radiation required forsterilization of the liquid under actual conditions that a materialsaving in power can be effected. It also follows that under theseconditions lamp life would be greatly extended.

The foregoing example while being an extreme case neverthelessemphasizes the significant gain even under other conditions. Whentreating waste water for instance, the influent conditions may vary fromhour to hour, daily or seasonally. If all factors remain the same andonly the influent turbidity changes from an absorption coeffienent of0.005 to 0.5, a ten-fold energy difference would be experienced. Theforegoing assumes a constant flow rate though in actual practice theflow rate will also vary materially and this of course would greatlyfurther modify the power requirements. If conductivity, such as metalliccontent, pH and the like of the water, should change, this would furtherincrease the ratio of power required between the socalled ideal andworst conditions. Under these combined circumstances, it is possible tohave an energy ratio as great as 15,000 to 1 though in practicalapplication such an energy ratio would be excessive for economic andsize reasons and therefore practical limits would be imposed onpermissible variables. Notwithstanding such limits, significant gains inefficiency of one or two orders of magnitude can readily be realizedover known methods and apparatus. From the foregoing, it becomeseminently apparent why known large volume devices and methods, all ofthe brute force type, are extremely limited in their application to lowflow, clear liquid systems and therefore under more severe conditionsare not cost effective as a means for practical disinfection orsterilization as evidenced from the following Table I and FIG. 9 of thedrawings.

                  TABLE I                                                         ______________________________________                                                  PERCENT                                                                       ENERGY REQUIRED                                                                     Worst          Ideal                                                          Case           Case                                                           Maxi-          Mini- Nomi- Maxi-                                              mum            mum   nal   mum                                Variable                                                                             Range    Power   Nominal                                                                              Power Range Range                              ______________________________________                                        Lamp life                                                                            10,000   100%    90%    80%   1.11:1                                                                              1.25:1                                    hours                                                                  Lamp   60.8° F.                                                                        100%    50%    33%   2:1   3:1                                temper-                                                                              to                                                                     ature  104° F.                                                         Ultra- 100%     100%    75%    50%   1.33:1                                                                              2:1                                violet to                                                                     trans- 50%                                                                    mission                                                                       jacket                                                                        Flow   100%     100%    35%     5%   2.85:1                                                                              20:1                               rate   to                                                                            25%                                                                    Influent                                                                             Absorp-  100%    25%    10%   4:1   10:1                               Turbidity                                                                            tion                                                                          Coef.                                                                         .005 to                                                                       0.5                                                                    Influent                                                                             .005 to  100%    25%    10%   4:1   10:1                               Chem-  0.5                                                                    istry                                                                         TOTAL ENERGY RATIO       135:1   15000:1                                      ENERGY RATIO WITH        12:1    75:1                                         CONSTANT FLOW AND                                                             INFLUENT CHEMISTRY                                                            ______________________________________                                    

Table I lists a plurality of variables such as lamp life etc., the totalrange of each said variables and the energy required under the worst,nominal and ideal conditions. The worst case requires the use of maximumavailable energy to properly sterilize a liquid under the most adverseconditions that may be experienced in a specific application. The idealcase requires the least power while the nominal case represents thenormal changes of the variables from the worst case that could beexpected in actual practice. The percentages shown for each of thevariables indicates that part of the total power required in each of thethree case if all other variables remained constant. Thus, if the flowrate dropped from an estimated maximum flow to a nominal or average flowthe energy requirement would be reduced to 35% of the maximum energyrequired. The final columns in the table show the power ratio for eachof the variables with the column entitled "Nominal Range" being theratio of the worst case to the nominal case and the column entitled"Maximum Range" being the ratio of the worst case to the ideal case.

The energy reductions indicated for the variables are conservativeestimates and in the case when all of the variables change so thatenergy requirements are reduced from the worst case to the nominal case,the resultant energy is reduced to 1/135 of the energy required for theworst case. In many applications, extremely wide variations can beexperienced in each of the variables. This may occur chiefly inindustrial plants where waste water is generally filtered and thensterilized prior to disposal. In such cases, composition of the water,flow rate, solid content and the like can vary over extremely widelimits and at greatly varying periodicities. Should the ideal case existfor even short periods of time, it would be possible to reduce theenergy requirement to 1/15000 of the power required for the worst case.It is therefore evident that in any application, including the treatmentof drinking water, variations in flow and water characteristics will beexperienced with the result that this invention will effect savings inenergy not heretofore considered possible or even probable.

Taking an even more conservative view of conditions that may exist inactual practice and assume that liquid flow and chemistry remainconstant, a 12:1 gain in energy savings is realized with variations fromthe worst case to the nominal case while the energy ratio from the worstcase to the ideal case is 75:1. Since the apparatus in accordance withthe invention functions to change energy requirements far more rapidlythan changes in any of the variables can occur, maximum operatingefficiency is maintained at all times. It is therefore evident that withthis invention substantial energy savings can be effected and at thesame time effective sterilization attained.

A typical example of the power demand to meet variations normallyexperienced in the use of ultraviolet radiation for the sterilization ofliquids is shown in FIG. 9. The illustrated graph is hypothetical butnevertheless closely approximates conditions existing in actualapplications wherein the flow rate and liquid quality are constant. Forthe first hour or more of operation, it is assumed that the influent isideal, that is, relataively clear. This portion of the graph is denotedby A and it will be noted that even under such conditions smallvariations such as turbidity and the like are present. These variationsare sensed by the apparatus in accordance with the invention and theenergy imparted to the liquid follows these variations and accordinglyaffords some energy reduction.

Section B of the graph illustrates the increase of energy required foran increase in turbidity which in this case is approximately 1800 watts.Section C of the graph indicates a further two or three fold increase inenergy required as a result of deposits on the protective jacketssurrounding the lamps after several hundreds of hours of operation.Section D of the graph represents the increase in power, approximatelytwo-fold, should lamp temperature drift to either side of a normal valuefor most efficient lamp operation. At this point, the power requirementshave now increased from 200 watts to over 10,000 watts as the result ofchanges in only three variables. Section E of the graph shows theprobable increase in power required due to aging of the lamps andpossibly other changes with the result that a maximum constant power of15,000 watts would be required to insure proper sterilization in priorart uncontrolled systems.

Section F of the graph showns a reduction in power as the result ofadjustment of lamp temperature. It will be observed that the mereadjustment of lamp temperature reduces power from a value in excess of10,000 watts to below 4,000 watts. Section G of the graph represents agradual increase in power because of lamp aging and correspondsessentially to graph section E.

It will be observed that the repetitive variations occuring a section Aof the graph shown in FIG. 9 actually continue throughout the entiregraph. Since, as pointed out above, the apparatus in accordance with theinvention senses these variations more rapidly than they occur, theenergy imparted to the liquid will also fluctuate and provide therequired radiation intensity to effect the desired sterilization. Thus,a further saving of energy is realized throughout the entire process.

In the foregoing description of the invention, four ultraviolet lampsare employed for sterilization of the fluid and under these conditionsthe flow rate would normally be at a reduced value and limitations wouldof course be placed on turbidity and conductivity. It is evident,however, that apparatus in accordance with the invention may employ anynumber of ultraviolet radiation sources and that the sources may be ofany desired size and configuration. For instance, in the treatment ofturbid waste water, it is conceivable that hundreds of ultraviolet lampswould be employed with each of the lamps being controlled in accordancewith the invention in order to insure reliable operation of theapparatus. At the same time, should conditions occur which would notrequire operation of all of the lamps, the apparatus would automaticallyinactivate one or more lamps not required to effect sterilization.

It is apparent from the foregoing that the lamps 44 through 47 can becontrolled in a variety of ways. One procedure is to provide for thesimultaneous control of the intensity of all lamps in accordance withfluid flow and characteristics as previously described. A more importantprocedure which affords a significant improvement in efficiency andprovides greater latitude of operation involves independent control ofeach lamp. With such an arrangement, the intensities of the lamps areindividually controlled whereby one lamp, for instance, may be at a highintensity while the remaining lamps may be at the same or differentreduced intensities. Under these conditions, the apparatus can handle,more precisely, a far wider range of fluid conditions and thus effect afurther material improvement in efficiency.

The invention heretofore described provides for the control of theradiation intensity in response to fluid characteristics and flowrelative to monitored operating conditions of the lamps. In certainapplications, it may be desirable to maintain substantially uniformultraviolet radiation intensity and modify the fluid flow in response tofluid characteristics. For this purpose, an electrically operated flowcontrol valve 110 (FIGS. 1 and 8), having control conductors 111, iscoupled to the inlet conduit 12. The flow control valve 110 is connectedby means of a driving amplifier 112 to the multiplex gates 84. With thisarrangement and by appropriately programming the control 71, fluidcharacteristics as well as the condition of the lamps and the intensityof the radiation penetrating the fluid will function to control thefluid flow rate to insure proper sterilization of the fluid.

It is well known that chemical disinfection using chemicals such aschlorine for instance is widely used in industry and generallyconstitutes the principal means for disinfecting drinking water. Notonly is chlorine relatively expensive and the apparatus for controllingthe admission of chlorine into a liquid system costly, but chlorine inquantities presently required materially and adversely affects the tasteof drinking water and in addition has been found to be a cancer causingagent. Chlorine is also generally considered a disinfecting agent ratherthan a sterilizing agent and thus has little, if any, affect on someviruses. It has been suggested that it is possible to utilize bothultraviolet sterilization and chemical disinfection which utilizes theadvantages of both systems, namely sterilization and continueddisinfection. With this invention, it has been found that the cost ofwater treatment utilizing both ultraviolet radiation and chemicaltreatment is materially below the cost of either system alone. Based oninformation presently available, it has been determined that with acombined system chlorine requirements can be reduced to about one-tenthto one-fifteeth of the normal requirements and energy requirements forultraviolet radiation to about one-tenth to one-quarter of the energynormally required. Thus by using the combination of the two systems withthis invention, a profound synergistic is realized in that the cost canbe reduced to the order of 20 to 25 percent of the cost of either systemalone.

To achieve this end, an electrically operated chlorine control valve 113as shown in FIGS. 1 and 8 is connected by means of conductors 115 to themultiplex gates 84 through a driver amplifier 114. By appropriatelyprogramming the control 71, precise amounts of chlorine can be fed tothe fluid and at the same time coordinated with the ultravioletradiation to achieve the most economical operating conditions for fluidcharacteristics and flow.

While the term "sterilization" is broadly defined as the destruction ofall living organisms, the use of the term "sterilization" herein is alsointended to include the reduction of at least certain living organismsto a predetermined maximum count as well as disinfection which in thegeneral sense means the total or partial destruction of harmful livingorganisms.

While only one embodiment of the invention has been illustrated anddescribed, it is apparent that alterations, changes and modificationsmay be made without departing from the true scope and spirit thereof.

What is claimed is:
 1. Apparatus for destroying undesirable organisms in a fluid comprising at least one ultraviolet radiation source, a fluid chamber having an inlet and outlet at least partially surrounding said source for guiding said fluid into close proximity to said source to effect penetration of said fluid by said radiation, means at said inlet for measuring physical characteristics of said fluid including flow rate, means for sensing the radiation intensity of said source imparted to said fluid and the radiation intensity emerging from said fluid to determine the radiant energy absorbed by said fluid and means for regulating the relationship between fluid flow and radiation intensity of said source to impart a selected quantity of radiant energy to said fluid per unit volume thereof, said selected quantity being determined by the measured characteristics of the fluid.
 2. Apparatus for destroying undesirable organisms in a fluid comprising at least one ultraviolet radiation source, a fluid chamber having an inlet and outlet at least partially surrounding said source for guiding said fluid into close proximity to said source to effect penetration of said fluid by said radiation, means for measuring physical characteristics of said fluid including flow rate and turbidity, means for sensing at least the radiation intensity imparted to said fluid, means for measuring the radiation intensity emerging from said fluid, means for determining the radiant energy absorbed by said fluid, and means for regulating the relationship between fluid flow and radiation absorbed by said first to impart a selected quantity of radiant energy to said fluid per unit volume thereof, said selected quantity being determined by the measured characteristics of said fluid.
 3. Apparatus according to claim 2 including means for feeding a chemical disinfectant to said fluid, means for controlling the flow rate of said chemical and means for maintaining a preselected relationship between chemical flow and ultraviolet radiation imparted to said fluid per unit volume.
 4. Apparatus according to claim 2 including a plurality of radiation sources and the last said regulating means includes means for independently varying the relationship between fluid flow and energy imparted to said fluid by each of said sources.
 5. Apparatus according to claim 2 including means for varying the turbulence of said fluid flowing through said chamber.
 6. Apparatus according to claim 2 including an electronic filter interconnected with said radiation source to remove high frequency energy pulses such as switching transients and the like from the energy activating said source.
 7. Apparatus according to claim 2 including electronic means for periodically sampling said fluid flow rate, at least one additional characteristic of said fluid and operating conditions of said radiation source to produce a plurality of corresponding electric signals, and control means including an electronic computer having programming means therefor for weighing said electric signals to determine the energy per unit volume imparted to said fluid, comparing said energy imparted to said fluid with a preselected value and producing correction signals for control of said radiation source and electronic control means for said source connected to said computer and responsive to said correction signals to modify the intensity of said source to impart said selected quantity of energy per unit volume to said fluid.
 8. Apparatus according to claim 7 wherein said sampling means comprises a plurality of multiplex gates interconnected with said computer and operable in response thereto for sequentially and repeatedly feeding signals corresponding to each of said fluid conditions, fluid flow and operating conditions of said ultraviolet source to said computer for the generation of said correction signals for controlling the operation of said ultraviolet source.
 9. Apparatus according to claim 8 including fluid flow control means at said inlet, a second plurality of multiplex gates connected to said computer and to the electronic control means for said source, and fluid flow control means including an electronic control for varying fluid flows, said computer sequentially operating the last said gates to feed control signals to each of the last said control means to vary the relationship between source intensity and flow to impart a selected quantity of energy per unit volume to said fluid.
 10. Apparatus according to claim 9 including a control valve for feeding a chemical disinfectant into said fluid, and electronic control means coupled to the last said gates and to said control valve, said computer sequentially operating the last said gates to feed selected quantities of said chemical to said fluid in accordance with the energy imparted per unit volume of said fluid. 